1. Field of the Invention
The present invention relates to means to control a drive mechanism including a clutch and adapted to act in response to the heat in a prime mover such as a vehicle engine and to control drive of a vehicle accessory, such as a fan mechanism, including a controlled response actuator to engage the friction clutch.
2. Prior Art
The problem of controlling heat dissipation devices in connection with a vehicle engine or prime mover so as to keep the prime mover below a predetermined maximum temperature, and at the same time minimizing horse power losses due to operation of the heat dissipation device has resulted in a number of solutions. Prior approaches include those disclosed in U.S. Pat. Nos. 3,804,219 and 3,848,622 of common assignee which show a structure utilizing a separate pressure supply source to provide a temperature responsive and continuously modulated actuation of a clutch mechanism to drive a vehicle fan and the fan speed thus being varied with variations with temperature conditions by controlling continuously the actuating pressure. Other devices known in the art, provide for simple on-off devices, acting in response to temperature to actuate a switch and for shutters in connection with the heat exchange device which may open or close in response to temperature. It has been found that with the simpler devices known as on-off devices the sudden change in engagement or disengagement of the device results in a sudden horsepower loss or gain in the engine which may cause difficulty for the driver of the vehicle. Further, in an attempt to provide for devices which do not allow sudden changes in horse power loss rather complicated structures result which are expensive to manufacture.